Bonded anchors – application in hollow substrates

Hollow substrates will not only require a specific type of product, but also appropriate installation steps. Read on to learn more details. 

Operating principle of bonded anchors

Unlike conventional mechanical fixings, the operation of which is based on the forces of expansion, bonded anchors bond to the substrate by way of adhesion, i.e. the surface bonding of materials. How does a bonded anchor work? Resin adheres uniformly to both the substrate and the component being fixed (typically a threaded rod). For that reason, when using bonded anchors, you can avoid generating stresses in the material, which proves particularly important when installing in weaker hollow substrates. 

Hollow substrates – pros and cons

According to the most general classification, base materials can be broken down into solid concrete and masonry substrates. One of masonry materials (next to solid blocks) is ceramic hollow brick, which comes in the following variations: 

• perforated brick
• hollow clay tile
• cinder block 

Hollow materials are made from clay, silt, and lightweight fillers (e.g. slag, expanded clay). Ceramic hollow bricks are used for the construction of single- and multi-family houses, public utility buildings, load bearing walls and partition walls. Being very versatile and popular, hollow substrates can be encountered not only during professional construction work, but also in simple home installation jobs. 

Ceramic hollow brick is characterised by low tensile and compressive strength. Being full of voids, this kind of base material displays lower strength: the more porous the material, the weaker it is. At the same time, hollow blocks show good thermal insulation properties, which makes them very popular in the construction industry. 

Bonded anchors for hollow substrates – which one to choose?

When choosing a bonded anchor, always make sure that the product you intend to use is suitable for the substrate in which you are about to fix. You can find detailed information on this matter in the product datasheet as well as in the relevant European Technical Approval (ETA). Importantly, not all bonded anchors are suitable for masonry materials. The most versatile polyester resins are definitely used most extensively, as they can be applied in non-cracked concrete, but also in solid as well as hollow bricks, hollow masonry units, concrete blocks, natural stone, or aerated concrete. The method of testing anchors in masonry substrates has been specified in European guidelines ETAG 029. 

Using polyester anchors in hollow substrates. Step-by-step installation instructions

If you are about to fix in hollow clay blocks using bonded anchors, keep in mind that the installation will generally not differ much from the application in concrete. The most important difference involves resin dispensing into the hole. Hollow materials require using a mesh sleeve, without which resin would simply flow down, making it impossible to effectively embed the rod in the hole. The weakest part of a load-generating system based on a hollow substrate is the substrate itself. For this reason, the anchor pressed through the mesh should work with the material and distribute the load evenly over as much of the substrate area as possible, thereby reinforcing the substrate structure at the anchorage point. This is a major advantage of resins, since conventional mechanical anchors can actually damage the material structure by applying expansion forces. 

Find out how to proceed when fixing in hollow substrates using bonded anchors:

Hole drilling

The first step in the installation of a bonded anchor is hole drilling. Importantly, if you are fixing in a masonry substrate, make sure to use a drill bit specifically designed for this type kind of base material. Also, do not use percussion drilling.